The present invention relates to automatically controlling continuously variable headlamps to prevent excessive glare seen by drivers in front of the headlamps.
Recently, headlamps producing a continuously variable illumination range have become available. The illumination range may be varied by one or both of changing the intensity of light and changing the direction of light emitted by the headlamps.
Varying headlamp illumination intensity can be accomplished in several different means. A first means is to provide a pulse-width modulated (PWM) signal to the headlamp. By varying the duty cycle of headlamp power, the headlamp illumination intensity can be increased or decreased. This may be accomplished by providing a PWM signal from a control system to a high power field effect transistor (FET) in series with the headlamp bulb.
Another means of varying the power duty cycle of a headlamp is to provide a PWM signal to a lamp driver integrated circuit such as a Motorola MC33286. This integrated circuit provides the added advantage of limiting the maximum inrush current to the headlamp, thus potentially extending the life of the headlamp bulb.
Yet another means of varying headlamp illumination uses high intensity discharge (HID) headlamps. HID lamps are a new, highly efficient headlamp technology. The ballasts used to power HID headlamps can be directly supplied with a control signal to vary headlamp illumination intensity.
Still another means to vary the illumination intensity of a headlamp is to provide an attenuating filter to absorb some of the light emitted from the headlamp. An electrochromic filter may be placed in front of the headlamp. By controlling the voltage applied to the electrochromic filter, the amount of light absorbed and, hence, the emitted illumination level, can be varied.
There are also several means available for changing the direction of light emitted from headlamps. Headlamp aim can be varied using actuators to move the headlamp housing relative to the vehicle. Typically, these actuators are electric motors such as stepper motors.
For headlamps with appropriately designed reflectors, mechanically moving the light source relative to the reflector can change headlamp beam direction as well as headlamp illumination intensity.
HID headlamps provide several additional methods of aiming the headlamp beam. Some of these methods involve deflecting or perturbing the arc in such a way as to vary the lamp output. U.S. Pat. No. 5,508,592 entitled xe2x80x9cMETHOD FOR DEFLECTING THE ARC OF AN ELECTRODELESS HID LAMPxe2x80x9d to W. Lapatovich et al., which is hereby incorporated by reference, describes exciting the HID lamp with a high-frequency radio signal. Modulating the signal causes the lamp to operate at an acoustic resonance point, perturbing the arc from its quiescent position. An alternative technique, known as magnetodynamic positioning (MDP), uses a magnetic field to shape the HID arc. MDP is being developed by Osram Sylvania Inc. of Danvers, Mass.
A collection of methods for implementing continuously variable headlamps is described in Society of Automotive Engineers (SAE) publication SP-1323 entitled xe2x80x9cAutomotive Lighting Technology,xe2x80x9d which is hereby incorporated by reference.
Automatic control of continuously variable headlamps offers several potential benefits over automatic control of traditional on-off headlamps. Greater flexibility for illumination is available, allowing headlamp illumination to be better adapted to driving conditions. Also, continuously varying the headlamp illumination does not create rapid changes in illumination that may startle the driver. Various methods have been devised to control both continuously variable and conventional discrete headlamps. One of the oldest methods is to aim the headlamp in the same direction as steered wheels. Another method increases the illumination range in proportion to increasing vehicle speed.
Still another method of controlling headlamps has been developed for HID lamps. The increased brightness and bluish color of the HID lamps is particularly disrupting to oncoming drivers. Due to this disruptness effect, certain European countries require headlamp leveling systems if HID lamps are used on a vehicle. These headlamp leveling systems detect the pitch of the vehicle relative to the road and adjust the vertical aim of the headlamps accordingly. Advanced systems further use the speed of the vehicle to anticipate small pitch disturbances caused by acceleration.
One problem with current continuously variable headlamp control systems is the inability to consider oncoming or leading vehicles in determining the illumination range of headlamps. One prior art device is expressed in U.S. Pat. No. 4,967,319 entitled xe2x80x9cHEADLIGHT APPARATUS FOR AUTOMOTIVE VEHICLExe2x80x9d by Y. Seko. This device utilizes vehicle speed along with the output from a five-element linear optical sensor array directly coupled to a headlamp. The headlamp incorporates motor drives to adjust the elevational angle of illumination beams. This design requires a separate sensing and control system for each headlamp or suggests as an alternative a controlled headlamp only on the side of the vehicle facing opposing traffic. This design presents many problems. First, the optical sensor and associated electronics are in close proximity to the hot headlamp. Second, placing the image sensor on the lower front portion of the vehicle may result in imaging surfaces being coated with dirt and debris. Third, placing the image sensor close to the headlamp beam makes the system subject to the masking effects of scattered light from fog, snow, rain, or dust particles in the air. Fourth, this system has no color discriminating capability and, with only five pixels of resolution, the imaging system is incapable of accurately determining lateral and elevational locations of headlamps or tail lights at any distance.
What is needed is control of continuously variable headlamps based on detection of oncoming headlamps and leading tail lights at distances where headlamp illumination would create excessive glare for the drivers of oncoming and leading vehicles.
The present invention may control continuously variable headlamps based on detected headlamps from oncoming vehicles and tail lights from leading vehicles. The control system may determine the proper aim of headlamps in steerable headlamp systems and may determine the proper intensity of headlamps in variable intensity headlamp systems. Gradual changes in the region of headlamp illumination may be supported. The control system also operates correctly over a wide range of ambient lighting conditions.
The headlamp control system of the present invention may determine the proper aim of headlamps in steerable headlamp systems.
The headlamp control system of the present invention may vary the intensity of headlamp beams continuously in response to detected oncoming and leading vehicles.
The headlamp control system of the present invention may operate such that the transition from high beam to low beam or from low beam to high beam is gradual and thus not startling to the vehicle driver.
The present invention also provides control of continuously variable headlamps over a wide range of ambient lighting conditions.
In carrying out the above objects and features of the present invention, a method for controlling continuously variable headlamps is provided. The method includes detecting an ambient light level. The continuously variable headlamps are set to daylight mode if the ambient light level is greater than a first threshold. The headlamps are set to low beam mode if the ambient light level is less than the first threshold but greater than a second threshold. Automatic headlamp dimming is enabled if the ambient light level is less than the second threshold.
In an embodiment of the present invention, automatic headlamp dimming includes obtaining an image in front of the headlamps. The image covers a glare area including points at which a driver in a vehicle in front of the headlamps would perceive the continuously variable headlamps as causing excessive glare if the headlamps were at full range. The image is processed to determine if the vehicle is within the glare area. If the vehicle is within the glare area, the continuously variable headlamp illumination range is reduced. Otherwise, the continuously variable headlamps are set to full illumination range. In various refinements, the continuously variable illumination range may be modified by changing the intensity of light emitted, by changing the direction of light emitted, or both.
In another embodiment of the present invention, reducing the continuously variable headlamp illumination range includes incrementally decreasing the illumination range. Obtaining the image, processing the image, and incrementally decreasing illumination range are repeated until the illumination range produces a level of illumination at the oncoming or leading vehicle position that would not be perceived as causing excessive glare by the driver in the vehicle in front of the continuously variable headlamps.
In still another embodiment of the present invention, the ambient light level is determined by a multipixel image sensor having an elevational angle relative to the controlled vehicle having continuously variable headlamps. The method includes acquiring a sequence of images, finding a stationary light source in each image, calculating a measure of elevation for the stationary light source in each image, and determining the elevational angle based on the calculated measures of elevation.
In a further embodiment of the present invention, the full illumination range is reduced if at least one form of precipitation, such as fog, rain, snow, and the like, is detected.
In a still further embodiment of the present invention, each continuously variable headlamp has an effective illumination range varied by changing vertical direction aimed. Each effective illumination range has an elevational direction corresponding to an upper extent of the headlamp beam bright portion. The method further includes acquiring a sequence of images. The elevational direction is determined for at least one continuously variable headlamp in each image of the sequence. A determination is then made as to whether or not the sequence of images was taken during travel over a relatively straight, uniform surface. If so, the determined elevational directions are averaged to obtain an estimate of actual elevational direction.
A system for controlling at least one continuously variable headlamp on a controlled vehicle is also provided. Each continuously variable headlamp has an effective illumination range varied by changing at least one parameter from a set including horizontal direction aimed, vertical direction aimed, and intensity emitted. The system includes an imaging system capable of determining lateral and elevational locations of headlamps from oncoming vehicles and tail lamps from leading vehicles. The system also includes a control unit that can acquire an image from in front of the at least one headlamp. The image covers a glare area including points at which the driver of a vehicle in front of the headlamps would perceive the headlamps as causing excessive glare. The image is processed to determine if at least one vehicle including oncoming vehicles and leading vehicles is within the glare area. If at least one vehicle is within the glare area, the headlamp illumination range is reduced. Otherwise, the headlamp illumination range is set to full illumination range.
In an embodiment of the present invention, the controlled vehicle has at least one low beam headlamp with variable intensity and at least one high beam headlamp with variable intensity. The control unit reduces the illumination range by decreasing the intensity of the high beam headlamp while increasing the intensity of the low beam headlamp.
In another embodiment of the present invention wherein headlamps produce illumination through heating at least one filament, the control unit causes a low amount of current to flow through each filament when the controlled vehicle engine is running and when the headlamp containing the filament is not controlled to emit light. The low amount of current heating the filament decreases filament brittleness thereby prolonging filament life.
In still another embodiment of the present invention, the imaging system is incorporated into the rearview mirror mount. The imaging system is aimed through a portion of the controlled vehicle windshield cleaned by a windshield wiper.
In yet another embodiment of the present invention, the controlled vehicle has a headlamp with a variable vertical aim direction. The system further includes at least one sensor for determining vehicle pitch relative to the road surface. The control unit aims the headlamp to compensate for controlled vehicle pitch variations. In a refinement, the controlled vehicle includes a speed sensor. The control unit anticipates controlled vehicle pitch changes based on changes in controlled vehicle speed.
In a further embodiment of the present invention, the controlled vehicle includes headlamps with variable horizontal aim direction. The control unit determines if a leading vehicle is in a curb lane on the opposite side of the controlled vehicle from oncoming traffic and is in the glare area. If no leading vehicle is in one of the curb lanes, headlamp illumination range is reduced by aiming the headlamps away from the direction of oncoming traffic.
In a still further embodiment of the present invention, the control unit reduces headlamp illumination range at a predetermined rate over a predetermined transition time.
A system is also provided for controlling at least one continuously variable headlamp having an effective illumination range varied by changing vertical direction aimed. Each effective illumination range has an elevational direction corresponding to an upper extent of the headlamp beam bright portion. The system includes an imaging system capable of determining lateral and elevational locations of headlamps from oncoming vehicles. The imaging system is mounted a vertical distance above each headlamp. The system also includes a control unit for acquiring an image in front of the headlamps. The image covers a glare area including points at which the driver of the oncoming vehicle would perceive the continuously variable headlamps to cause excessive glare. The image is processed to determine if at least one oncoming vehicle is within the glare area. If at least oncoming vehicle is within the glare area, the elevational angle between the imaging system and the headlamps of each of the at least one oncoming vehicles is determined. If at least one oncoming vehicle is within the glare area, the continuously variable headlamps are aimed such that the elevational direction is substantially parallel with a line between the imaging system and the headlamps of the oncoming vehicle producing the greatest of the determined elevational angles.
A system is further provided for controlling continuously variable headlamps. The system includes at least one moisture sensor for detecting at least one form of precipitation such as fog, rain, and snow. The system also includes a control unit to reduce the headlamp full illumination range when precipitation is detected.
These and other features, advantages, and objects of the present invention will be further understood and appreciated by those skilled in the art by reference to the following specification, claims, and appended drawings.